English - Nooteboom Giants on the Road Magazine English - Nr. 6 - 2019 | Page 52

GIANTS ON THE ROAD History HYDRAULIC SUSPENSION A LARGE PART OF NOOTEBOOM TRAILERS ARE EQUIPPED WITH HYDRAULIC SUSPENSION AS STANDARD. THIS USED TO BE DIFFERENT, BECAUSE UNTIL THE LATE SEVENTIES MOST TRAILERS WERE STILL FITTED WITH LEAF SPRINGS. THE MANDATORY LOAD-DEPENDENT BRAKING FORCE DIRECTIVES, INTRODUCED IN 1976, CHANGED THIS. In just a few years, advanced air suspension and hydraulic suspension systems were developed and the trailers with leaf spring suspension disappeared from the European roads. Nooteboom delivered the first trailer with hydraulic suspension in 1975 and improved the system time and time again during the past decades. Many Nooteboom customers opt for hydraulic suspension because the stability – particularly with a load that has a high centre of gravity – is better than other suspension systems. BACK IN TIME Around 1970 nearly every trailer had robust leaf spring assemblies that functioned very well, even if the trailer was significantly overloaded. The regulation of the braking force was done via a simple valve: empty, half empty or full. In the EEG there were already regulations in force in 1971 to improve the braking of trucks and trailers. In October 1976 the directive 75/524/EEG was introduced. The most important task for the trailer manufacturers: the brake power balance must from now on adjust automatically to the load of the trailer. On trailers with leaf spring suspension the braking power is regulated via the spring deflection of the leaf spring assembly. This method is not very exact because old- fashioned trailers have a very short suspension stroke, sometimes no more than a few centimetres. Moreover, after some time the leaf springs tend to ‘settle’, so that the brake pressure regulator ‘thinks’ that the trailer is always loaded. Air suspension and hydraulic suspension give a much better signal. But it still took more than ten years before the coordination between the tractor and trailer functioned properly. Hydraulic suspension was a huge step forward, not only because of the effective brake pressure regulator, but also because the old trailers with leaf spring suspension were notorious for their bumpy rides. 52 PRINCIPLE AND OPERATION With hydraulic suspension a hydraulic cylinder is placed between the axle and chassis. The cylinder itself does not provide the suspension, but it is connected to an expansion tank which is partly filled with nitrogen gas, the accumulator. By compressing the gas in the accumulator the axle can move up and down. The cylinders of the suspension on either side of the trailer are connected, so that the hydraulic pressure in the cylinders and the pressure on each wheel is more or less the same. The hydraulic circuit of the suspension can also be connected to a hydraulic adjustable gooseneck. THE CLEVER SOLUTIONS OF NOOTEBOOM The axle housing at the front has two short parabolic springs. The short, wedged-in springs act as a stabiliser that increases the rolling resistance when the trailer is cornering. The cylinder of the suspension is secured in a particular way on both sides. On the axle there is a removable ball joint that prevents the hydraulic cylinder from bending, which can cause it to leak. On the chassis side there is a spherical bearing that also allows the cylinder to move in transverse direction. Both the ball joint and spherical bearing are essential constructive elements for a long lifespan. THE ACCUMULATOR The accumulator, which is partly filled with nitrogen gas, takes care of the suspension. By combining various accumulators the trailer will have a comfortable suspension, whether fully loaded or empty. The first accumulator (from 15 bar) comes into action with an empty trailer and the other one (from 60 bar) with a loaded trailer. An additional advantage of hydraulic suspension is that no shock absorbers are required.